Methods and apparatus for detecting possible repeated handover different radio access technologies

ABSTRACT

Inter-radio access technology (IRAT) ping pong handover of a user equipment (UE) connection between a source radio access technology (RAT) communications network, e.g., LTE, and a different target RAT communications network, e.g., UTRAN, is detected. A control node determines IRAT ping pong handover information and evaluates an IRAT handover request message for the UE connection from the source RAT network with respect to the handover ping pong information. Based thereon, the node determines that the UE connection meets one or more ping pong conditions associated with the handover ping pong information and provides an indication of an IRAT ping pong handover condition to a base station in the source RAT network to allow the base station to make mobility adjustments.

TECHNICAL FIELD

This technology relates to radio communications involving differentradio access technologies (RATs).

INTRODUCTION

As shown in FIG. 1, the Long Term Evolution (LTE) and GSM EDGE RadioAccess Network/Universal Terrestrial Radio Access Network (GERAN/UTRAN)architectures communicate via interfaces between core network nodes ofeach respective technology. See 3GPP TS 23.401, the contents of whichare incorporated herein by reference. One of the ways for the LTE andGERAN/UTRAN technologies to communicate with each other is via the RadioInformation Management (RIM) protocol, which allows transfer ofinformation from LTE to GERAN/UTRAN in a pre-configured manner, asspecified in 3GPP TS 48.018, the contents of which are incorporatedherein by reference. A specific type of RIM interaction is defined toavoid unnecessary handovers from LTE to GERAN/UTRAN networks.Unnecessary handovers are often referred to as ping pong handovers.Herein, a handover or a UE handover refers to handover of a UEconnection.

FIG. 2 shows an example of handover (HO) ping pong between a first radioaccess network (RAN) base station using a first type of radio accesstechnology (RAT) referred to as RAT 1 and a second RAN base stationusing a second different type of radio access technology (RAT) referredto as RAT 2. Each of the base stations is associated with a respectivecore network node. Depending on the type of radio access network (RAN)which characterizes the base stations, the core network nodes can be orcomprise, for example, a Serving GPRS Support Node (SGSN) node for aUTRAN network or a Mobility Management Entity (MME) for an E-UTRAN orLTE type of network. One or both/more core network nodes comprise ahandover ping pong detector and a UE context memory 44. The handoverping pong detector determines whether a UE connection is in a handoverping pong scenario. The handover ping pong detector ascertains whetherthe UE is in a handover ping pong scenario by using history informationconcerning the UE, and particularly history information, which comprisesa list L representing handover events that occurred in the past forwireless terminal 30. The history list L is maintained and updated asappropriate by the network core networks which serve the base stationsto which the UE travels. In this example, FIG. 2 shows list L beingtransferred from one core network node to another core network node inconjunction with a most recent handover of the UE culminating in storageof list L in UE context memory.

FIG. 3 shows a message sequence chart for an Unnecessary IRAT Handoverprocedure currently included in 3GPP TS 48.018, TS 36.413, and TS25.413, all of which are incorporated herein by reference.

The LTE radio access network (RAN) configures specific measurementcriteria and thresholds for handing over a UE connection from LTE,(i.e., an LTE base station is referred to as an eNB), to a Radio NetworkController (RNC) coupled to a NB2 in cell 2 in GERAN/UTRAN, (aGERAN/UTRAN base station is referred to as a NodeB or NB). Themeasurement configuration is provided in the following message named theIRAT Measurement Configuration IE in 3GPP TS.25.413.

The configuration in FIG. 4 is sent by an LTE node to a UTRAN/GERAN nodevia the Source BSS to Target BSS Transparent Container IE (in a case ofhandover to GERAN, see TS 48.018) or via the Source RNC to Target RNCTransparent Container IE (in case of handover to UTRAN, see TS 25.413)within the handover signalling, i.e., as part of the HANDOVER REQUIREDmessage generated in LTE (as shown in step 1 and step 2 of FIG. 1 a).Upon reception of this configuration, the UTRAN/GERAN needs to configurethe UE handed over from LTE to perform UE measurements for a timeduration equal to the Measurement Duration IE and over the E-UTRANfrequencies indicated in the E-UTRA frequencies IE. The LTE cells forwhich UE measurements are taken are sent to and recorded by the targetUTRAN/GERAN base station if the measurement results are abovepreconfigured thresholds specified in the RSRP IE and RSRQ IE. If themeasurements performed by the UE fulfill the configured thresholds forthe whole measurement duration, then the RNC will trigger an unnecessaryIRAT handover indication by means of delivery of an HO REPORT messagefrom GERAN/UTRAN to E-UTRAN (see step 5 of FIG. 1 a) if the following issatisfied (excerpted from TS 25.413):

-   -   The cells for which all UE measurements received during the        indicated period of time exceeded the threshold if any. In case        there is no source RAT cell whose measurement results exceed the        threshold for the whole measurement duration, but a group of        source RAT cells together provide coverage that fulfils the        threshold during the whole measurement period, HO Report should        also be triggered, in which the cells that exceed the threshold        in the first UE measurement report are included. If both        thresholds are present, the received radio measurements must        exceed both the RSRP and the RSRQ thresholds in order to satisfy        the indicated radio conditions.

As it can be seen from the quote above, the HO Report IE will begenerated only if reported measurements satisfy the configuredthresholds for the whole duration of the configured measurement window.If all the conditions are satisfied, then the HO Report IE sent fromUTRAN/GERAN to LTE via RIM is constructed as follows (see TS 36.413):

In the HO Report IE, the Cells reported in the Candidate Cell List IEare the LTE cells providing good enough coverage, while the HO Target IDIE is the cell towards which handover can be avoided while in LTE.

A new scenario must be addressed as part of the Self Organizing Network(SON) Enhancements Work Item Description (WID). This scenario isdescribed as follows in R3-120400: “In inter RAT mobility, a ping pongHO is understood as a handover from a source cell in a source RAT (A) toa target cell in a target RAT (B) different from the source RAT, andwhere the UE is being handed over back to a cell in the source RAT (A)within a ‘definable limited time.’ Additionally, the case when the stayat the target RAT is still within the ‘definable limited time,’ but theUE passes through more than one cell before handing over to the sourceRAT, should also be considered as an inter-RAT ping-pong.”

The scenario above can be readily detected if the UE hands over fromUTRAN/GERAN to LTE and back to UTRAN/GERAN because the assumption byRAN3 for ping pong detection is that the ping pong event is detectedonly if the UE comes back to a cell in the same radio networkcontroller/base station subsystem (RNC/BSS) domain.

During a ping pong handover scenario of typeUTRAN/GERAN—LTE—UTRAN/GERAN, the UE History Information IE will be sentin a transparent container from LTE to the final target UTRAN/GERANRNC/BSS as part of the handover signaling. From this IE, the targetUTRAN/GERAN RNC/BSS can deduce that the UE moved from UTRAN/GERAN to LTEand back to UTRAN/GERAN. Hence, the UTRAN/GERAN Radio Network System(RNS) can adjust mobility configuration parameters towards the specificLTE cell involved in the ping pong event and prevent a similar ping pongevent from reoccurring.

But in the case of ping pong from LTE to GERAN/UTRAN and back to LTE,the ping pong effect is not avoided using an UE History Information IEor using LTE RNS internal analysis. Consider the example in FIG. 6 whichshows a UE affected by a E-UTRAN->UTRAN->E-UTRAN handover ping pong.FIG. 6 also introduces cells. A cell corresponds to an area served by abase station at a specific carrier frequency using a specific radioaccess technology (RAT). The base station 1 serves cell in this exampleusing E-UTRAN RAT, and therefore, the base station is denoted as aneNB1. The base station 2 serves cell2 in the example using UTRAN RAT,and therefore, the base station is denoted NB2. The NB2 is controlled bya radio network controller (RNC) denoted as RNC2. The base station 3serves cell3 in the example using E-UTRAN RAT, and therefore, the basestation is denoted eNB3). Handover of a UE connection is referred to asbetween cells, although it is understood that nodes serve and controlcells and are responsible for handover functions and signaling. Here,the UE may handover to a Cell3 served by the eNB3 from the source Cell1where the ping pong mobility was initiated. In this case, it is notpossible to deduce at the source eNB (eNB1) that the ping pong occurredneither the UE History Information IE reach the source eNB1, nor eNB1knows whether the ping pong event is avoidable or not. The problem istherefore how to ensure efficient detection and resolution of the pingpong effect described in this scenario.

In R3-120400, a brief description of possible solutions to this problemwas presented. However, those solutions are based on the definition ofeither a new X2 procedure or modification of an existing procedure, andthus, are not efficient due to their high impact on existing eNBs andinterfaces. A simpler more efficient solution is therefore desirable.

SUMMARY

Methods and apparatus are described for detecting a possible inter-radioaccess technology (IRAT) ping pong handover of a user equipment (UE)connection between a source radio access technology (RAT) communicationsnetwork and a different target RAT communications network. In an IRATping pong handover, the UE connection is handed over from a first cellin the source RAT network to a second cell in the target RAT network andthen handed over back to a third cell in the source RAT network within apredetermined limited time during which coverage for the UE connectionis available from the source RAT network. A control node associated withthe target RAT network may be configured to perform the following:determining IRAT ping pong handover information, evaluating the UEconnection related to an IRAT handover request message from the sourceRAT network with respect to the IRAT ping pong handover information,based on the evaluating, determining that the UE connection meets one ormore ping pong conditions associated with the IRAT ping pong handoverinformation, and providing an indication of an IRAT ping pong handovercondition to a base station in the source RAT network.

The IRAT ping pong handover may involve different base stations in thesource RAT network, in which case, the control node provides theindication of the IRAT ping pong handover condition to a handover sourcebase station in the source RAT network.

In some example embodiments, the determining step includes receiving theIRAT handover request message from a source base station in the sourceRAT network that includes IRAT measurement configuration information, UEhandover measurement time period information, and IRAT handover timeperiod information. The determining step further includes determiningthat the UE connection is to be handed back over to the source RATnetwork before the UE handover measurement time period has expired andbefore the IRAT handover time period has expired. In an exampleapplication, the source RAT network is an LTE network, the target RATcommunications network is a UTRAN network, the control node is a RadioNetwork Controller (RNC). The RNC receives from the first cell ahandover required/reloation request message that includes the IRATmeasurement configuration information, the UE handover measurement timeperiod information, and the IRAT handover time period information, andsends a Radio Information Management (RIM) Request transfer message tothe first cell that includes a handover report having a IRAT ping ponghandover information element. The RNC may send the RIM messageindependently of whether an IRAT handover ping pong of the UE connectionoccurs. The RNC may also send the handover report to a base stationserving the first cell to allow that base station to adjust mobility orhandover settings associated with the second cell and/or target RATnetwork to avoid a future hand over of the UE connection to the secondcell. The handover report may include a HO Report Type informationelement (IE) or a HO type IE that includes an IRAT ping pong handoverindicator.

In another example embodiment, the control node adjusts handover ormobility parameters associated with the third cell and/or with thesource RAT network, which are used to configure UE measurements andreport triggering.

In another example embodiment, the IRAT ping pong handover indication issent from a base station serving the third cell to a base stationserving the first cell.

In some example embodiments where the IRAT ping pong handover involvesdifferent base stations in the source RAT network, the control nodeprovides the indication of the IRAT ping pong handover condition to ahandover target base station in the source RAT network for subsequentdelivery to a handover source base station in the source RAT network toallow the handover source base station to adjust mobility or handoversettings associated with the second cell and/or the target RAT networkto avoid a future hand over of the UE connection to the second cell.

In an example implementation, the source RAT network is an LTE network,the target RAT communications network is a UTRAN network, and thecontrol node is a Radio Network Controller (RNC). The RNC sends to thethird cell a relocation request acknowledgement/handover message thatincludes the IRAT ping pong handover indication in a target to sourcetransparent container information element (IE) to allow the third cellto provide the IRAT ping pong handover indication to the first cell.

In another example implementation, where the source RAT network is anLTE network, the target RAT communications network is a UTRAN network,and the control node is a Radio Network Controller (RNC), the RNCreceives from a base station serving the first cell a handoverrequired/relocation request message that includes an IRAT ping pongtrigger information element (IE) and an IRAT ping pong timer IE in asource to target transparent container.

In some example embodiments, the control node includes an IRAT ping pongtimer. The control node determines that the UE connection is handed overfrom the first cell in the source RAT network to the second cell in thetarget RAT network and determines an IRAT ping pong occurrence if ahandover of the UE connection occurs to the source RAT network beforethe IRAT ping pong timer expires and coverage for the UE connection isavailable from the source RAT network. In an example implementationwhere the source RAT network is an LTE network, the target RATcommunications network is a UTRAN network, and the control node is aRadio Network Controller (RNC), the RNC sends an IRAT ping pongindication to the third cell via a target to source transparentcontainer to allow a base station serving the third cell to send an IRATping pong indication message to the first cell. In an alternativeexample implementation, the RNC sends a RELOCATION REQUESTACKNOWLEDGEMENT message to a core network (CN) node and sending an IRATping pong indication to the first cell via a Radio InformationManagement (RIM) Request Transfer message.

In some example embodiments, the control node receives an IRAT ping ponghandover detection time window from an operations and maintenance node.

Another example embodiments provide methods and apparatus for detectinga possible inter-radio access technology (IRAT) ping pong handover of auser equipment (UE) connection between a source radio access technology(RAT) communications network and a different target RAT communicationsnetwork. A base station associated with the first cell in the source RATnetwork sends a handover or cell relocation request message to a controlnode associated with the target RAT communications network, receives anindication of an IRAT ping pong handover condition if the UE connectionmeets one or more ping pong conditions associated with the handover pingpong information, and adjusts mobility parameters with respect to thesecond cell and/or to the target RAT network to avoid a future handoverof the UE connection to the second cell.

In an example implementation where the source RAT network is an LTEnetwork, the target RAT communications network is a UTRAN network, andthe control node is a Radio Network Controller (RNC), the handover orcell relocation request message includes IRAT measurement configurationinformation and UE handover measurement time period information. Thebase station receives a Radio Information Management (RIM) Requesttransfer message that includes a handover report having an IRAT pingpong handover information element. The handover or cell relocationrequest message may include IRAT handover time period information. Thebase station may receive an IRAT ping pong handover indication from abase station serving the third cell. The first and third cells may bethe same cell or different cells.

The base station may determine statistical information concerning IRATping pong handover over an observation time period and sending thedetermined statistical information to an operations and maintenancenode.

In yet another example embodiment, an operations and maintenance node isconfigured to communicate with a source radio access technology (RAT)communications network and a different target RAT communicationsnetwork. The operations and maintenance node includes data processingcircuitry configured to:

receive statistical information determined by one or more control nodesconcerning IRAT handover ping pong events during an observation timeperiod;

determine an IRAT handover ping pong detection time window based on thereceived statistical information;

provide the determined IRAT handover ping pong detection time window toenable a network control node to detect an IRAT handover ping pongsituation for a user equipment (UE) connection and take action to avoidfurther IRAT ping pong handover of the UE connection,

where in an IRAT ping pong handover, the UE connection is handed overfrom a first cell in the source RAT network to a second cell in thetarget RAT network and then handed over back to a third cell in thesource RAT network within a predetermined limited time.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates in function block form a UTRAN/LTE combinedArchitecture;

FIG. 2 is a function block diagram illustrating an example oftransferring a history log for a UE from one core network node toanother core network node;

FIG. 3 illustrates an example signaling diagram for a 3GPP-basedunnecessary handover detection procedure;

FIG. 4 illustrates an example configuration of a 3GPP-based IRATMeasurement Configuration information element (IE);

FIG. 5 illustrates an example configuration of a 3GPP-based HO Report IEmessage;

FIG. 6 shows an example of ping pong handover of a UE connection from aLTE network to a UTRAN network and back to the LTE network;

FIGS. 7A and 7B are flowcharts that illustrates non-limiting exampleprocedures for use in detecting a possible IRAT ping pong handover of aUE connection;

FIG. 8 illustrates an example configuration of a 3GPP-based HO Report IEmessage in accordance with a first non-limiting example embodiment;

FIG. 9 illustrates an example message sequence for IRAT ping pongdetection in accordance with a first non-limiting example embodiment;

FIG. 10 illustrates an example message sequence for IRAT ping pongdetection in accordance with a second non-limiting example embodiment;and

FIG. 11 illustrates function block diagrams of a UE, source basestation, target base station, RNC, and core network nodes in accordancewith one non-limiting example embodiment.

DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS

The following sets forth specific details, such as particularembodiments for purposes of explanation and not limitation. But it willbe appreciated by one skilled in the art that other embodiments may beemployed apart from these specific details. In some instances, detaileddescriptions of well known methods, nodes, interfaces, circuits, anddevices are omitted so as not obscure the description with unnecessarydetail. Those skilled in the art will appreciate that the functionsdescribed may be implemented in one or more nodes using hardwarecircuitry (e.g., analog and/or discrete logic gates interconnected toperform a specialized function, ASICs, PLAs, etc.) and/or using softwareprograms and data in conjunction with one or more digitalmicroprocessors or general purpose computers. Nodes that communicateusing the air interface also have suitable radio communicationscircuitry. Moreover, the technology can additionally be considered to beembodied entirely within any form of computer-readable memory, such assolid-state memory, magnetic disk, or optical disk containing anappropriate set of computer instructions that would cause a processor tocarry out the techniques described herein.

Hardware implementation may include or encompass, without limitation,digital signal processor (DSP) hardware, a reduced instruction setprocessor, hardware (e.g., digital or analog) circuitry including butnot limited to application specific integrated circuit(s) (ASIC) and/orfield programmable gate array(s) (FPGA(s)), and (where appropriate)state machines capable of performing such functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer, processor, and controller may be employedinterchangeably. When provided by a computer, processor, or controller,the functions may be provided by a single dedicated computer orprocessor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

A cell is associated with a base station, where a base station comprisesin a general sense any node transmitting radio signals in the downlink(DL) and/or receiving radio signals in the uplink (UL). Example basestations are a NodeB, eNodeB, eNB, macro/micro/pico radio base station,home eNodeB, relay, repeater, sensor, transmitting-only radio nodes orreceiving-only radio nodes. A base station may operate or at leastperform measurements in one or more frequencies, carrier frequencies orfrequency bands and may be capable of carrier aggregation. It isunderstood that the problem described in the background is not limitedto the LTE, UTRAN, and GERAN radio access technologies (RATs). Indeed,the problem may occur among any RATs to which a UE is allowed tohandover. Thus, although the description below is in the example contextof LTE, UTRAN, and GERAN radio access technologies (RATs), they are onlyexample, and the technology may be applied to other RATs and inter-RAThandover scenarios.

Although the description is given for user equipment (UE), it should beunderstood by the skilled in the art that “UE” is a non-limiting termcomprising any wireless device or node equipped with a radio interfaceallowing for at least one of: transmitting signals in UL and receivingand/or measuring signals in DL. Some examples of UE in its general senseare a PDA, a laptop, a mobile radio station, a sensor, a fixed relay, amobile relay, and a radio network node (e.g., an LMU or a femto basestation or a small base station using the terminal technology). A UEherein may comprise a UE (in its general sense) capable of operating orat least performing measurements in one or more frequencies, carrierfrequencies, component carriers or frequency bands. UEs here can operateusing different RATs.

The technology provides methods and apparatus for detecting repeatedhandover (handover ping pong) of a UE connection between different radioaccess technologies. A control node associated with a first type of RAT,e.g., an RNC in a UTRAN network, receives or otherwise determineshandover ping pong information such as a handover ping pongconfiguration or one or more handover ping pong criterion. That controlnode evaluates an incoming UE connection handover from a seconddifferent network with a second different type of RAT, e.g., an eNB in aLTE network, with respect to the handover ping pong information todetermine if that UE connection meets one or more ping pong conditionsassociated with the handover ping pong information. If so, the controlnode provides an indication of a handover ping pong condition to a basestation in the second network, e.g., an eNB in the LTE network.

In an example embodiment where the ping pong involves different basestations in the second network, the control node provides the indicationof handover ping pong condition to a handover source base station in thesecond network.

In another example embodiment where the ping pong involves differentbase stations in the second network, the control node provides theindication of handover ping pong condition to a handover target basestation in the second network which then relays that indication ofhandover ping pong condition to a handover source base station in thesecond network.

FIGS. 7A and 7B are flowcharts that illustrate non-limiting exampleprocedures for use in detecting a possible IRAT ping pong handover of aUE connection. FIG. 7A illustrates example steps performed at a networkcontrol node for detecting a possible inter-radio access technology(IRAT) ping pong handover of a user equipment (UE) connection between asource radio access technology (RAT) communications network and adifferent target RAT communications network. As explained above, in anIRAT ping pong handover, the UE connection is handed over from a firstcell in the source RAT network to a second cell in the target RATnetwork and then handed over back to a third cell in the source RATnetwork within a predetermined limited time, even though the UEconnection could be served by the source RAT during the time it is beingserved by the target RAT. The network control node, which is associatedwith the target RAT network, determines IRAT ping pong handoverinformation (step S1), and evaluates an IRAT handover request messagefor the UE connection from the source RAT network with respect to thehandover ping pong information (step S2). The evaluation may includereceiving UE measurements to determine that the UE connection could beserved by the source RAT during the time it is being served by thetarget RAT. Based on the evaluating, the control node determines thatthe UE connection meets one or more ping pong conditions associated withthe handover ping pong information (step S3) and provides an indicationof an IRAT ping pong handover condition to a base station in the sourceRAT network (step S4).

FIG. 7B illustrates example steps performed at the source base stationfor detecting a possible IRAT ping pong handover of the UE connection.Initially, the source base station sends a handover or cell relocationrequest message, which may include a Measurement Configurationinformation element (IE) aimed at configuring IRAT UE measurements for acertain duration, to a control node associated with the target RATcommunications network (step S10). One option is that the source basestation has received information for the configuration of theMeasurement Configuration IE from an Operations and Maintenance node(OaM). The base station subsequently receives an indication of an IRATping pong handover condition if the UE connection meets one or more pingpong conditions associated with the handover ping pong information (stepS12). The base station may then adjust mobility parameters with respectto the second cell or target RAT network to avoid a future ping pong andunnecessary handover of the UE connection to the second cell (step S14).

A non-limiting example handover ping pong illustration for a UEconnection is from LTE to UTRAN/GERAN and back. But again, thetechnology may be used for other scenarios involving different source ortarget RATs. The technology can use an inter-RAT (IRAT) unnecessaryhandover function (or similar function) to flag or otherwise indicatethe occurrence of an LTE→UTRAN/GERAN→LTE ping pong handover scenario. Inthis example scenario, when a UE connection is handed over from LTE toUTRAN/GERAN, and a measurement configuration is sent to the UTRAN/GERANnetwork for detection of IRAT handovers, two cases can occur. First, UEmeasurements collected by the UTRAN/GERAN network during the configuredmeasurement duration window can satisfy predetermined unnecessaryhandover conditions. In this first case, a Radio Information Management(RIM) message containing a HO Report IE (see FIG. 7 described below) issent back to the LTE network so that future handovers to the sameUTRAN/GERAN cell can be avoided. The RIM message is preferably sentindependently of whether the UE connection hands over back toUTRAN/GERAN, e.g., independently from whether an IRAT handover ping pongoccurs. In the second case, while collecting measurements withinUTRAN/GERAN and before expiration of the measurement duration window,the UE connection is handed over back to the LTE network. If thehandover back to LTE happens within a short enough time, this eventconstitutes an IRAT ping pong. Although to date there is no provisionfor the HO Report IE to be sent to the LTE network, which means that themeasurements collected by the UTRAN/GERAN RNS are lost, the technologyin this application allows delivery of the HO Report IE back to the LTEnetwork also in this second case described above. Specifically, the LTEcells detected while the UE connection is being handled in UTRAN/GERANare reported, and the HO Target ID IE is also reported in cases wherethe UE hands over back to LTE before a measurement duration windowexpires. The HO Report IE sent in this case may be enhanced with a newIE to indicate the occurrence of IRAT ping pong. Alternatively, adedicated handover ping pong indication may be sent from UTRAN/GERAN toLTE after the target RAT identifies the handover ping pong event.Further, the handover ping pong indication may be sent via a dedicatedX2 message from the target LTE eNB to the source LTE eNB once the UEconnection hands over back to LTE.

The triggering of the handover ping pong detection may be performedeither immediately or over a time period. Triggering may also beperformed on a statistical basis, i.e., in case a pre-set number ofhandover ping pong instances have occurred or if a pre-set number ofinstances have occurred in a pre-set time window.

As an example of how to distinguish that an HO Report IE is sent even incases when the measurement period is interrupted by an handover to LTE,namely to distinguish this case from other cases of unnecessary IRAThandover detection, a new value for the HO Report Type IE or HO type IEmay be introduced as shown in FIG. 8. For example, the new value may benamed “Early IRAT Handover.” The table below shows a HO Report IE, wherethe new value for the HO Report Type IE is included. The new value mayalso be included in the HO Type IE (although not shown in this example).

By adding a new value to the HO Report Type IE or to the HO Type IE, theLTE eNB receiving the HO Report IE can determine that the report doesnot refer to measurements covering the entire measurement durationconfigured in the IRAT Measurement Configuration IE, but instead, thatthe report refers to a case where a new inter RAT handover towards LTEoccurred within the measurement interval corresponding to themeasurement duration and the measurements up to the handover occurrencehave fulfilled the thresholds set in the IRAT Measurement ConfigurationIE.

A handover ping pong event includes at least two IRAT handovers, e.g.,between LTE and the same UTRAN/GERAN Radio Network Subsystem (RNS),occurring in a defined window of time. A handover ping pong detectiontime window referred to in the examples below is calledT_(IRATPingPong). With respect to FIG. 6, a window timerT_(IRATPingPong) is started either at the source base station eNB 1 inLTE, when a UE handover is triggered towards UTRAN/GERAN, or at the RNC2in UTRAN/GERAN, when a UE handover is completed from LTE. At this time,a first example embodiment assumes that measurements for an unnecessaryIRAT handover are configured.

Taking FIG. 6 as an example scenario, if the UE connection, after beinghanded over from LTE Cell1 to UTRAN Cell2, is then handed over to LTECell 3 before the Measurement Duration timer window configured in theIRAT Measurement Configuration IE has expired and before theT_(IRATPingPong) timer window has expired, then a HO Report is sent fromRNC2 to eNB1.

FIG. 9 below shows a non-limiting example of a detailed message exchangebetween the nodes in the non-limiting example described in FIG. 6 forthis first non-limiting example embodiment. In FIG. 9, the LTE eNB1decides to handover the UE connection to UTRAN/GERAN Cell2. The LTE eNB1can optionally decide to start the handover ping pong detection timewindow T_(IRATPingPong). The handover signaling towards the UTRAN/GERANRNC2 shown in step 1 contains the IRAT Measurement Configuration IE.Once the Relocation Request message (as part of Handover signaling) isreceived, the RNC2 may optionally decide to start T_(IRATPIngPong).

The decision to configure and start timer T_(IRATPingPong), and totrigger and evaluate IRAT measurements, i.e., the decision to detectIRAT ping-pong handovers (independently of whether IRAT ping-ponghandover detection is performed in the target RAT or the source RAT) maybe taken at every IRAT handover instance, during a given time period, orthat decision may be based on a pre-configured ratio of UE connectionsthat are handed back to the source RAT within a preconfigured time afterhandover to the target RAT measured in the source RAT. Hence, until theT_(IRATPingPong), timer is triggered and IRAT ping pong detection isactivated, it is only known that UE connections are being handed back tothe source RAT within a certain time period, but it is not possible toknow whether the handover back to the source RAT was due to a coveragehole or due to a ping-pong handover.

The Source-to-Target Transparent Container received by the target RATnode (e.g., RNC2) in the RELOCATION REQUEST message may also contain theT_(IRATPingPong) parameter. Doing so ensures that the source RAT (e.g.,LTE) and target RAT (e.g., UTRAN/GERAN) are coordinated in evaluatingwhen a handover ping pong event is to be triggered.

The RNC2 also configures the UE to perform measurements using an IRATMeasurement Configuration IE. From the handover signalling from the LTEeNB1, the UTRAN/GERAN RNC2 can understand that the UE is coming from anLTE RAT.

During the time when the UE connection is handled by Cell2, if ahandover of that UE connection to LTE occurs from any of the cellsserved by the UTRAN/GERAN RNC2 before the T_(IRATPingPong) expires,then, if the measurements collected by the UE fulfill the configuredIRAT ping pong threshold(s) specified in the Measurement ConfigurationIE, the RNC2 generates a RIM transfer to the LTE eNB1 including an HOReport with the information collected until the handover from Cell2 toCell3 was executed or until the Measurement Duration timer expired.

In one example embodiment, the UE in UTRAN may be configured to takeIRAT measurements on LTE cells even when the IRAT MeasurementConfiguration IE is not present in the Source to Target TransparentContainer IE. In this case, the target RAT (RNC2) configures the UE andincludes the measurement results in an HO Report IE int eh RIM requesttransfer message, where the Measurement Duration and thresholds can beconfigured by the target RAT (RNC2). If the UE measurements fulfill theIRAT ping pong configured thresholds, then the HO Report IE can be sentback to the source RAT (eNB1) via a RIM Request message.

One example way to interpret reception of such HO Report is for the LTEeNB1 to deduce that the HO Report (not including any new IEs) was sentto indicate that an IRAT Ping Pong event of the LTE-UTRAN-LTE type. Thisis possible because eNB1 receives the HO Report before the MeasurementDuration expires and/or before T_(IRATPingPong) expires. For anotherexample approach, the HO Report may contain a new information element(IE) that explicitly flags or indicates the occurrence of an IRAT PingPong of the LTE-UTRAN-LTE type. The new IE can be named “IRAT Ping Pong”as one example, and it can be a Boolean variable.

Once the IRAT Ping Pong event is flagged to the LTE eNB1, which analyzesthe information contained in the HO Report, the LTE eNB1 can deduce thetarget cell for which the ping pong occurred, i.e., UTRAN Cell2 in thisexample. The LTE eNB1 can thus adjust its mobility parameter setting(s)towards that target cell in order to avoid future IRAT ping pongoccurrences. Mobility parameters may include parameters that are used toconfigure UE measurements and report triggering. Once the IRAT ping ponghandover is detected, the target RAT (RNC2) may also apply correctionsto the mobility parameters towards the LTE target cell to avoidtriggering such IRAT ping-pong handovers.

To adjust the mobility parameters that cause IRAT ping-pong handovers,the source LTE eNB1 may store a radio resource control (RRC) UE contextfrom which it can determine the reasons for the IRAT handover. If thehandover was not due to, for example coverage, then the informationabout the ping pong may be separated from handovers related to coveragein this example. A non-coverage example is handovers due to loadbalancing between radio access technologies. So one example way ofhandling this information is to consider IRAT handover ping ponginformation when evaluating load balancing but not when the reason forhandover is coverage for the UE connection.

Another example is where the UE is moved from LTE to a lower frequencytarget RAT (e.g., UTRAN) because of the UE moving at high speed and inorder to improve signal robustness. Once in the target RAT, the UE mightbe handed over back to LTE either because of a change in the UE speed orbecause of an error in configuration of handover parameters. Byretrieving the UE context, the source eNB (e.g., eNB 1) can determinewhat the handover cause was and can react appropriately, e.g., thesource eNB can adjust hysteresis parameters when handing over a highspeed UE to a lower frequency RAT. Also, the target RAT (e.g., UTRANRNC2) can apply measures to avoid handover back to source RAT. Oneexample way to do this is to only adjust the mobility parameters for UEhandover to LTE that happened shortly after a handover from LTEoccurred.

Moreover, the operations and maintenance (OaM) system may configureT_(IRATPingPong), e.g., based on one or more predetermined factors suchas the time needed for adequate measurements, the UE contextperseverance time on the LTE source side, the cost of lost packets inthe transport network, etc. Such configuration may be also performed andadjusted by the operator or defined a priori. Furthermore, the eNBand/or the RNC may store statistics about the ping pong events andnon-ping pong events, and if desired, aggregate them into one or morereports and provide the report(s) to the OaM system. The aggregation maybe implemented using for example counters and histograms.

In a second non-limiting example embodiment shown in FIG. 10, the sourceRAT (e.g., LTE eNB1) does not rely on IRAT Unnecessary Handoverdetection to detect an IRAT Ping Pong event. Instead, the source RATincludes one or more new IEs in a Source to Target Transparent Containersent via 51: HANDOVER REQUIRED. Such one or more new IEs may include aPing Pong Detection trigger and/or an IRAT Ping Pong Timer (Step 1). Theconfiguration of these IEs may have been obtained from an OaM node. Thetarget RAT node (e.g., RNC2) may decide to configure the UE withmeasurements on cells in the source RAT, or the target RAT node may basethe ping pong evaluation on handover occurrence, i.e., on whether the UEhands over back to the source RAT within the T_(IRATPingPong) timer.

By knowing that the first handover was from LTE, the RNC2 can detectIRAT ping pong if a handover towards LTE occurs from any of the RNC2'sserved UTRAN/GERAN cells before T_(IRATPingPong) expires. In this case,two options are now described. First, either at a ping pong eventoccurrence or after a number of ping pong events is detected (possiblywithin a preset time window), the RNC2 sends an IRAT ping pongindication to LTE eNB3 via a Target to Source Transparent Container instep 2. Message 3a follows which includes a new X2 message forindicating an IRAT ping pong. As a second option, either at a ping pongevent occurrence or after a number of ping pong events is detected(possibly within a preset time window), the RNC2 sends a RELOCATIONREQUEST ACKNOWLEDGEMENT to the core network (CN). Further, the RNC2sends an IRAT ping pong indication to the LTE eNB1 via a dedicated RIMRequest Transfer message as shown at message 3b.

Example actions and signaling that may be taken by eNB1, RNC2, and eNB3to avoid future occurrence of the IRAT ping pong are similar to thosedescribed in the first example embodiment.

In a third non-limiting example embodiment, the source RAT (e.g., eNB1)does not include a new or specific IE in the Source to TargetTransparent Container IE in the HANDOVER REQUIRED/RELOCATION REQUESTmessage. Instead, the target RAT (e.g., RNC2) autonomously decides totrigger a preconfigured T_(IRATPingPong) timer. The target RAT (e.g.,RNC2) can receive the timer T_(IRATPingPong) from an OaM node. Byknowing that the first handover was from LTE, the RNC2 can detect IRATping pong if a handover towards LTE from any of its served cells occursbefore T_(IRATPingPong) expires. The target RAT (RNC2) may decide toconfigure the UE with measurements on the source RAT (LTE), or it maybase the ping pong evaluation on handover occurrence, i.e., on whetherthe UE hands over back to the source RAT within the T_(IRATPingPong)timer. In this case, two options are now described. First, either atping pong event occurrence or after a number of ping pong events isdetected monitored (possibly within a preset time window), the RNC2sends an IRAT ping pong indication to the eNB3 via a Target to SourceTransparent Container in step 2. This is followed by message 3a whichincludes a new X2 message for indication of IRAT ping pong. For a secondoption, either at ping pong event occurrence or after a number of pingpong events is detected (possibly within a preset time window), the RNC2sends a RELOCATION REQUEST ACKNOWLEDGEMENT to the core network (CN).Further, the RNC2 sends an IRAT ping pong indication to the eNB1 via adedicated RIM message.

Example actions that may be taken by eNB1 and RNC2 to avoid futureoccurrence of the IRAT ping pong are similar to those described in thefirst example embodiment.

In another example embodiment, an operations and maintenance (OaM) nodethat communicates with at least the source RAT communications network,e.g., LTE, receives statistical information determined by one or morebase stations and/or RNCs concerning IRAT handover ping pong eventsduring an observation time. The IRAT handover ping pong event generationcould be based on inter-node signaling as has been disclosed above. Sofor example, the eNB1, eNB3, and/or RNC gather such statistical dataover the observation time period and send it to the OaM node. The OaMnode determines an IRAT handover parameter reconfiguration based on thereceived statistical information and provides the determined IRAThandover parameter reconfiguration to avoid or reduce further IRAT pingpong handover of UE connections. Example OaM actions and signaling toavoid future occurrence of the IRAT ping pong are similar to thosedescribed in the example embodiments above for a radio network node.

FIG. 11 shows a source base station 28 _(S) with RAT 1 corresponding inthis example to an LTE eNB and a target base station 28 _(T) with RAT 2corresponding in this example to a UTRAN NodeB. An operations andmaintenance (OaM) node 10 is shown that includes a data processing andcontrol unit 12 coupled to one or more network interfaces 14 forcommunicating with one or more core networks 16, RNC 26, and basestations 28. For example the OaM node 10 may receive statistical and/orperformance information relating to IRAT handover ping pong from the RNC26 and/or base stations 28 and may configure one or more IRAT handoverping pong parameters like T_(IRATPingPong), e.g., based on one or morepredetermined factors such as the time needed for adequate measurements,the UE context perseverance time on the LTE source side, the cost oflost packets in the transport network, etc.

FIG. 11 also shows general aspects of UE 30 and selected functionalitiesof the source base station 28 _(S) and candidate base station 28 _(C).The UE includes a data processing and control unit 31 for controllingvarious operations required by the UE. The data processing and controlunit 31 includes a mobile terminal inter-RAT/frequency handover function40 and measurement communication function 42. In addition, the dataprocessing and control unit 31 provides control signals as well as datato an appropriate radio transceiver 33 connected to one or more antennas35. There may be different transceivers for different RATs or aconfigurable transceiver configured to communicate with a current RAT.The measurement communication function 42 controls communications withsource base station 28 _(S) and target base station 28 _(T) whenrequesting or obtaining measurements or information (e.g., measurementsor information for potential handover purposes) are concerned. Theinter-RAT/frequency handover function 40 is invoked when it isdetermined that a handover is to occur.

Both source base station 28 _(S) and target base station 28 _(T)comprise a base station data processing and control unit 36, which isconnected to one or more base station radio transceivers (TX/RX) 38.Each base station transceiver (TX/RX) 38 is connected to a correspondingantenna 39, an appropriate one of which communicates over an airinterface with the UE 30.

The data processing and control unit 36 of the source base station 28_(S) includes inter-RAT/frequency handover function 50 and measurementcommunication function 52. For example, source base station 28 _(S)comprises inter-RAT/frequency handover function 50 _(S) and measurementcommunication function 52 _(S). Similar functionality is found in theradio network controller (RNC) 26 associated with the target basstation. The respective measurement communication function 52 controlscommunications with UE 30 for requesting or obtaining measurements orinformation (e.g., measurements or information for potential handoverpurposes); the respective inter-RAT/frequency handover function isinvoked when it is determined that a handover is to occur.

The example embodiments described herein may be considered asindependent embodiments or may be considered in any combination witheach other to describe non-limiting examples.

The technology offers many benefits. For example, the technology makesit possible to avoid undesirable inter-RAT handovers in situations thatknown inter-RAT ping pong techniques have fallen short.

Although the description above contains many specifics, they should notbe construed as limiting but as merely providing illustrations of somepresently preferred embodiments. For example, non-limiting, exampleembodiments of the technology were described in a context with LTE andGERAN/UTRAN technologies. But the principles of the technology describedmay also be applied to other radio access technologies and otherinter-RAT handover ping pong scenarios. Indeed, the technology fullyencompasses other embodiments which may become apparent to those skilledin the art. Reference to an element in the singular is not intended tomean “one and only one” unless explicitly so stated, but rather “one ormore.” All structural and functional equivalents to the elements of theabove-described embodiments that are known to those of ordinary skill inthe art are expressly incorporated herein by reference and are intendedto be encompassed. Moreover, it is not necessary for a device or methodto address each and every problem sought to be solved by the describedtechnology for it to be encompassed by the descried technology.

1. A method for detecting a possible inter-radio access technology(IRAT) ping pong handover of a user equipment (UE) connection between asource radio access technology (RAT) communications network and adifferent target RAT communications network, where in an IRAT ping ponghandover, the UE connection is handed over from a first cell in thesource RAT network to a second cell in the target RAT network and thenhanded over back to a third cell in the source RAT network within apredetermined limited time during which coverage for the UE connectionis available from the source RAT network, the method being implementedby a control node associated with the target RAT network and comprisingthe steps of: determining, by the control node, IRAT ping pong handoverinformation; evaluating the UE connection related to an IRAT handoverrequest message from the source RAT network with respect to the IRATping pong handover information; based on the evaluating, determiningthat the UE connection meets one or more ping pong conditions associatedwith the IRAT ping pong handover information; and providing anindication of an IRAT ping pong handover condition to a base station inthe source RAT network.
 2. The method in claim 1, wherein the IRAT pingpong handover involves different base stations in the source RATnetwork, the method comprising the control node providing the indicationof the IRAT ping pong handover condition to a handover source basestation in the source RAT network.
 3. The method in claim 1, wherein thedetermining step includes receiving the IRAT handover request messagefrom the source base station in the source RAT network that includesIRAT measurement configuration information, UE handover measurement timeperiod information, and IRAT handover time period information, whereinthe determining step includes determining that the UE connection is tobe handed back over to the source RAT network before the UE handovermeasurement time period has expired and before the IRAT handover timeperiod has expired.
 4. The method in claim 3, wherein the source RATnetwork is an LTE network, the target RAT communications network is aUTRAN network, the control node is a Radio Network Controller (RNC),wherein the method further comprises the RNC: receiving from the firstcell a handover required/reloation request message that includes theIRAT measurement configuration information, the UE handover measurementtime period information, and the IRAT handover time period information,and sending a Radio Information Management (RIM) Request transfermessage to the first cell that includes a handover report having a IRATping pong handover information element.
 5. The method in claim 4,wherein the RNC sends the RIM message independently of whether an IRAThandover ping pong of the UE connection occurs.
 6. The method in claim4, wherein the RNC sends the handover report to a base station servingthe first cell to allow that base station to adjust mobility or handoversettings associated with the second cell and/or the target RAT networkto avoid a future hand over of the UE connection to the second celland/or the target RAT network.
 7. The method in claim 4, wherein thehandover report includes a HO Report Type information element (IE) or aHO type IE that includes an IRAT ping pong handover indicator.
 8. Themethod in claim 3, wherein the control node adjusts handover or mobilityparameters associated with the third cell and/or with the source RATnetwork, which are used to configure UE measurements and reporttriggering.
 9. The method in claim 1, wherein the IRAT ping ponghandover indication is sent from a base station serving the third cellto a base station serving the first cell.
 10. The method in claim 1,wherein the IRAT ping pong handover involves different base stations inthe source RAT network, the method comprising the control node providingthe indication of the IRAT ping pong handover condition to a handovertarget base station in the source RAT network for subsequent delivery toa handover source base station in the source RAT network to allow thehandover source base station to adjust mobility or handover settingsassociated with the second cell and/or the target RAT network to avoid afuture hand over of the UE connection to the second cell.
 11. The methodin claim 1, wherein the source RAT network is an LTE network, the targetRAT communications network is a UTRAN network, the control node is aRadio Network Controller (RNC), wherein the method further comprises theRNC: sending to the third cell a relocation requestacknowledgement/handover message that includes the IRAT ping ponghandover indication in a target to source transparent containerinformation element (IE) to allow the third cell to provide the IRATping pong handover indication to the first cell.
 12. The method in claim1, wherein the source RAT network is an LTE network, the target RATcommunications network is a UTRAN network, the control node is a RadioNetwork Controller (RNC), wherein the method further comprises the RNCreceiving from a base station serving the first cell a handoverrequired/relocation request message that includes an IRAT ping pongtrigger information element (IE) and an IRAT ping pong timer IE in asource to target transparent container.
 13. The method in claim 1,wherein the control node includes an IRAT ping pong timer, the methodfurther comprising the control node: determining that the UE connectionis handed over from the first cell in the source RAT network to thesecond cell in the target RAT network; determining an IRAT ping pongoccurrence if a handover of the UE connection occurs to the source RATnetwork before the IRAT ping pong timer expires and coverage for the UEconnection is available from the source RAT network.
 14. The method inclaim 13, wherein the source RAT network is an LTE network, the targetRAT communications network is a UTRAN network, the control node is aRadio Network Controller (RNC), wherein the method further comprises theRNC sending an IRAT ping pong indication to the third cell via a targetto source transparent container to allow a base station serving thethird cell to send an IRAT ping pong indication message to the firstcell.
 15. The method in claim 13, wherein the source RAT network is anLTE network, the target RAT communications network is a UTRAN network,the control node is a Radio Network Controller (RNC), wherein the methodfurther comprises the RNC sending a RELOCATION REQUEST ACKNOWLEDGEMENTmessage to a core network (CN) node and sending an IRAT ping pongindication to the first cell via a Radio Information Management (RIM)Request Transfer message.
 16. The method in claim 1, wherein the controlnode receives an IRAT ping pong handover detection time window from anoperations and maintenance node.
 17. A control node for detecting apossible inter-radio access technology (IRAT) ping pong handover of auser equipment (UE) connection between a source radio access technology(RAT) communications network and a different target RAT communicationsnetwork, where in an IRAT ping pong handover, the UE connection ishanded over from a first cell in the source RAT network to a second cellin the target RAT network and then handed over back to a third cell inthe source RAT network within a predetermined limited time during whichcoverage for the UE connection is available from the source RAT network,the control node being associated with the target RAT network andcomprising data processing circuitry configured to: determine, by thecontrol node, IRAT ping pong handover information; evaluate the UEconnection related to an IRAT handover request message from the sourceRAT network with respect to the handover ping pong information; based onthe evaluating, determine that the UE connection meets one or more pingpong conditions associated with the handover ping pong information; andprovide an indication of an IRAT ping pong handover condition to a basestation in the source RAT network.
 18. The control node in claim 17,wherein the IRAT ping pong handover involves different base stations inthe source RAT network and the control node is configured to provide theindication of the IRAT ping pong handover condition to a handover sourcebase station in the source RAT network.
 19. The control node in claim17, wherein the control node is configured to: receive the IRAT handoverrequest message from a source base station in the source RAT networkthat includes IRAT measurement configuration information, UE handovermeasurement time period information, and IRAT handover time periodinformation, and determine that the UE connection is to be handed backover to the source RAT network before the UE handover measurement timeperiod has expired and before the IRAT handover time period has expired.20. The control node in claim 19, wherein the source RAT network is anLTE network, the target RAT communications network is a UTRAN network,the control node is a Radio Network Controller (RNC), wherein the RNC isconfigured to: receive from the first cell a handoverrequired/relocation request message that includes the IRAT measurementconfiguration information, the UE handover measurement time periodinformation, and the IRAT handover time period information, and send aRadio Information Management (RIM) Request transfer message to the firstcell that includes a handover report having a IRAT ping pong handoverinformation element.
 21. The control node in claim 20, wherein thehandover report includes a HO Report Type information element (IE) or aHO type IE that includes an IRAT ping pong handover indicator.
 22. Thecontrol node in claim 19, wherein the control node is configured toadjust handover or mobility settings associated with the third celland/or the source RAT network.
 23. The control node in claim 17, whereinthe source RAT network is an LTE network, the target RAT communicationsnetwork is a UTRAN network, the control node is a Radio NetworkController (RNC), wherein the RNC is configured to send to the thirdcell a relocation request acknowledgement/handover message that includesan IRAT ping pong handover indication in a target to source transparentcontainer information element (IE) to allow the third cell to providethe IRAT ping pong handover indication to the first cell.
 24. Thecontrol node in claim 17, wherein the source RAT network is an LTEnetwork, the target RAT communications network is a UTRAN network, thecontrol node is a Radio Network Controller (RNC), wherein the RNC isconfigured to receive from a base station serving the first cell ahandover required/relocation request message that includes an IRAT pingpong trigger information element (IE) and an IRAT ping pong timer IE ina source to target transparent container.
 25. The control node in claim17, wherein the control node includes an IRAT ping pong timer, thecontrol node configured to: determine that the UE connection is handedover from the first cell in the source RAT network to the second cell inthe target RAT network; determine an IRAT ping pong occurrence if ahandover of the UE connection occurs to the source RAT network beforethe IRAT ping pong timer expires.
 26. The control node in claim 25,wherein the source RAT network is an LTE network, the target RATcommunications network is a UTRAN network, the control node is a RadioNetwork Controller (RNC), wherein the RNC is configured to send an IRATping pong indication to the third cell via a target to sourcetransparent container to allow a base station serving the third cell tosend an IRAT ping pong indication message to the first cell.
 27. Thecontrol node in claim 25, wherein the source RAT network is an LTEnetwork, the target RAT communications network is a UTRAN network, thecontrol node is a Radio Network Controller (RNC), wherein the RNC isconfigured to send a RELOCATION REQUEST ACKNOWLEDGEMENT message to acore network (CN) node and sending an IRAT ping pong indication to thefirst cell via a Radio Information Management (RIM) Request Transfermessage.
 28. A method associated with detecting a possible inter-radioaccess technology (IRAT) ping pong handover of a user equipment (UE)connection between a source radio access technology (RAT) communicationsnetwork and a different target RAT communications network, where in anIRAT ping pong handover, the UE connection is handed over from a firstcell in the source RAT network to a second cell in the target RATnetwork and then handed over back to a third cell in the source RATnetwork within a predetermined limited time during which coverage forthe UE connection is available from the source RAT network, the methodbeing implemented by a base station associated with the first cell inthe source RAT network and comprising the steps of: sending, by the basestation, a handover or cell relocation request message to a control nodeassociated with the target RAT communications network; receiving anindication of an IRAT ping pong handover condition if the UE connectionmeets one or more ping pong conditions associated with the handover pingpong information; and adjusting mobility parameters with respect to thesecond cell and/or to the target RAT network to avoid a future handoverof the UE connection to the second cell.
 29. The method in claim 28,wherein the source RAT network is an LTE network, the target RATcommunications network is a UTRAN network, the control node is a RadioNetwork Controller (RNC), wherein the handover or cell relocationrequest message includes IRAT measurement configuration information andUE handover measurement time period information, and wherein the basestation receives a Radio Information Management (RIM) Request transfermessage that includes a handover report having an IRAT ping ponghandover information element.
 30. The method in claim 29, wherein thehandover or cell relocation request message includes IRAT handover timeperiod information.
 31. The method in claim 28, wherein the base stationreceives an IRAT ping pong handover indication from a base stationserving the third cell.
 32. The method in claim 28, further comprisingdetermining statistical information concerning IRAT ping pong handoverover an observation time period and sending the determined statisticalinformation to an operations and maintenance node.
 33. A source radioaccess technology (RAT) base station for use in detecting a possibleinter-radio access technology (IRAT) ping pong handover of a userequipment (UE) connection between a source radio access technology (RAT)communications network and a different target RAT communicationsnetwork, where in an IRAT ping pong handover, the UE connection ishanded over from a first cell in the source RAT network and served bythe source RAT base station to a second cell in the target RAT networkand then handed over back to a third cell in the source RAT networkwithin a predetermined limited time during which coverage for the UEconnection is available from the source RAT network, the source RAT basestation comprising: a transmitter configured to send a handover or cellrelocation request message to a control node associated with the targetRAT communications network; a receiver configured to receive anindication of an IRAT ping pong handover condition if the UE connectionmeets one or more ping pong conditions associated with the handover pingpong information; and a data processor configured to adjust mobilityparameters with respect to the second cell and/or to the target RATnetwork to avoid a future handover of the UE connection to the secondcell.
 34. The source RAT base station in claim 33, wherein the sourceRAT network is an LTE network, the target RAT communications network isa UTRAN network, the control node is a Radio Network Controller (RNC),wherein the handover or cell relocation request message includes IRATmeasurement configuration information and UE handover measurement timeperiod information, and wherein the base station receives a RadioInformation Management (RIM) Request transfer message that includes ahandover report having an IRAT ping pong handover information element.35. The source RAT base station in claim 33, wherein the base stationreceives an IRAT ping pong handover indication from a base stationserving the third cell.
 36. The source RAT base station in claim 33,wherein the first and third cells are the same cell.
 37. An operationsand maintenance node configured to communicate with a source radioaccess technology (RAT) communications network and a different targetRAT communications network, comprising data processing circuitryconfigured to: receive statistical information determined by one or morecontrol nodes concerning IRAT handover ping pong events during anobservation time period; determine an IRAT handover ping pong detectiontime window based on the received statistical information; provide thedetermined IRAT handover ping pong detection time window to enable anetwork control node to detect an IRAT handover ping pong situation fora user equipment (UE) connection and take action to avoid further IRATping pong handover of the UE connection, where in an IRAT ping ponghandover, the UE connection is handed over from a first cell in thesource RAT network to a second cell in the target RAT network and thenhanded over back to a third cell in the source RAT network within apredetermined limited time.